Blade for a gas turbine and casting technique method for producing same

ABSTRACT

A blade for a gas turbine has a leading edge and a trailing edge, and an interior cavity, which is delimited by internal surfaces, for guiding cooling air therethrough. A multiplicity of turbulators or pins, which are formed on the wall, are arranged in a distributed manner in the region of the trailing edge and project from the internal surfaces into the cavity, to improve the transfer of heat between the wall of the blade and the cooling air. An improvement of the internal cooling is achieved by the turbulators or pins extending into the cavity in a direction which can be freely selected within an angular range.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of International Application No. PCT/EP2009/056150, filed May 20, 2009, which claims priority to Swiss Patent Application No. 00898/08, filed Jun. 12, 2008, the entire contents of all of which are incorporated by reference as if fully set forth.

FIELD OF INVENTION

The present invention relates to the field of gas turbine technology. It refers to a blade for a gas turbine and a method for producing such a blade by a casting technique.

BACKGROUND

Blades of gas turbines, which are fastened either as rotor blades on the rotor or fastened as stator blades on the casing which encloses the rotor, are subjected to impingement by hot gas which comes from the combustor and are exposed to thermal loads in the process. These blades, in the course of improving the thermal efficiency, are increasingly exposed to circumferential flow at still higher turbine inlet temperatures. It is not to be ignored, therefore, that these blades have to be cooled internally and/or externally by a cooling medium, especially cooling air, being introduced preferably via the blade root into the hollow interior of the blade airfoil, cooling the blade internally there via convectively applied cooling methods or selectively by means of impingement cooling, and then being blown out into the hot gas flow, in order to carry out a so-called film cooling there if necessary on the external side of the blade. The cooling medium flows through the interior of the blade mostly in a plurality of cooling passages which are connected in a serpentine-like manner and extend through the blade airfoil in the radial direction.

When producing such a blade by a casting technique, a casting core, which forms and keeps the internal hollow cavity of the blade with the cooling passages free and further details during the casting of the blades, has to be created. For producing the casting core, use is made of a core mold assembled from two halves which during demolding of the finished casting core are drawn apart in a specified direction (see U.S. Pat. No. 5,716,192, for example). Contingent upon the direction in which the two mold halves have to be drawn apart, limitations ensue in the design of the casting core and therefore in the design of the cavity of the subsequent blade. These limitations play a role particularly in the case of complex shapes of the cavity, as are described in WO-A1-03/042503, for example. In order to create the cavity of the blade there, which cavity consists of various cooling circuits and a multiplicity of pins and turbulators, a plurality of casting cores are produced and combined with each other, which leads to a very costly production process.

SUMMARY

In a first aspect, the present disclosure is directed to a blade for a gas turbine. The blade includes a leading edge and a trailing edge, and an interior cavity, which is delimited by internal surfaces, for guiding cooling air therethrough. To improve the transfer of heat between the wall of the blade and the cooling air, a multiplicity of members, which are formed on the wall to improve cooling. The members are arranged in a distributed manner in the region of the trailing edge and project from the internal surfaces into the cavity. The members extend into the cavity in a direction which can be freely selected within an angular range.

In a second aspect, the present disclosure is directed to method for producing the above blade. The method includes, in a first step, providing a core mold for forming a casting core which keeps the cavity of the blade free. The method also includes, in a second step, producing the casting core by means of the core mold, in a third step, removing the casting core from the core mold and, in a fourth step, casting the blade by the casting core. The core mold which is provided in the first step comprises two mold halves, which during demolding are drawn apart in a first direction. At least one mold insert, which is provided for forming the members, is arranged in the mold halves in the trailing edge region. In the third step, after the parting of the mold halves in the first direction, the at least one mold insert is withdrawn from the formed casting core in a second direction which differs from the first direction.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention shall subsequently be explained in more detail based on exemplary embodiments in conjunction with the drawing. All elements which are not essential for the direct understanding of the invention have been omitted. Like elements are provided with the same designations in the various figures. In the drawings:

FIG. 1 shows in cross section in a greatly simplified view an exemplary embodiment of a blade according to the invention with turbulators or pins which project into the cavity perpendicularly to the wall surface in the region of the trailing edge;

FIG. 2 shows in section the simplified casting core for producing the blade from FIG. 1 by a casting technique;

FIG. 3 shows the problems which are associated with the mold halves of the core mold when producing the casting core from FIG. 2;

FIG. 4 shows in a view which is comparable to FIG. 3 a core mold, which is modified within the scope of the invention, with mold inserts for overcoming the limitations which are associated with the core mold according to FIG. 3, and

FIG. 5 shows one of the mold inserts from FIG. 4.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Introduction to the Embodiments

The invention should provide a remedy here. It is therefore an object of the invention to propose a blade which is improved with regard to internal cooling, overcoming certain limitations created by the casting core, and which at the same time can be produced with little additional cost. It is furthermore an object of the invention to disclose a method for producing such a blade.

The object is achieved by means of the entirety of the features of the independent claims. It is a feature of the invention that the turbulators or pins which are formed on the wall in the region of the trailing edge for improving the heat transfer between the wall of the blade and the cooling air extend into the cavity in a direction which can be freely selected within an angular range.

With regard to the cooling, it is particularly advantageous if, according to one development of the invention, the turbulators or pins extend into the cavity in a direction which is essentially perpendicular to the associated internal surface.

The method according to the invention for producing the blade by a casting technique, in which, in a first step, a core mold is provided for forming a casting core which keeps the cavity of the blade free, in a second step, the casting core is produced by means of the core mold, in a third step, the casting core is removed from the core mold, and in a fourth step, the blade is cast by means of the casting core. The core mold, which is provided in the first step, comprises two mold halves which during demolding are drawn apart in a first direction, wherein at least one mold insert, which is provided for forming the turbulators or pins, is arranged in the mold halves in the trailing edge region, and in the third step, after the parting of the mold halves in the first direction, the at least one mold insert is withdrawn from the formed casting core in a second direction which differs from the first direction.

In one development of the method according to the invention, the second direction is perpendicular to the internal surface which is associated with the turbulators or pins.

According to another development of the method, a plurality of mold inserts are arranged in the mold halves and during demolding of the formed casting core are withdrawn in different directions which differ from the first direction.

DETAILED DESCRIPTION

FIG. 1 shows, in cross section in a greatly simplified view, an exemplary embodiment of a gas turbine blade according to the invention. The blade 10 has an airfoil profile with a leading edge 11, a trailing edge 12 and also a (convex) suction side 13 and a (concave) pressure side 14. The blade 10 has a wall 15 which encloses a hollow cavity 16 which is used for the guiding of cooling air which inter alia can discharge into the outside space from cooling air outlets 17 which are provided at the trailing edge 12. The cavity 16 can be divided into a plurality of sub-chambers by means of one or more ribs 29.

For forming the cavity 16 and the details and elements which are arranged therein, a casting core 21 (FIG. 2), which has to be produced in advance, is required when producing the blade 10 by a casting technique. For producing the casting core 21, use is made as a rule of a core mold 23 according to the type shown in FIG. 3, which is assembled from two mold halves 23 a and 23 b which can separated along a parting plane 25 and which during demolding are drawn apart in the direction which is indicated by the arrows in FIG. 3. As a result of the specified direction, in which the two mold halves 23 a and 23 b have to be drawn apart during demolding (demolding direction), the orientation of specific elements in the cavity 16 of the blade is also indirectly determined via the casting core 21. Thus, the rib 29 in the cavity 16 of the blade extends inevitably in the demolding direction because the mold halves 23 a and 23 b with their corresponding rib elements 30 can only be withdrawn from the finished casting core in this way.

According to the invention, additional elements 18 in the cavity, which can be formed as (round) pins or (rib-like) turbulators and improve the transfer of heat between the cooling air which flows in the cavity 16 and the wall 15, are now arranged or formed in the trailing edge region of the blade 10. The direction in which the elements 18 project from the wall 15 into the cavity 16 should now be able to be selected within an angular range independently of the demolding direction of FIG. 3, i.e. the orientation of the elements 18 can differ from the orientation of the rib 29. In particular, the elements 18, for fluidic reasons, are intended to be perpendicular to the internal surface 19 or 20 of the wall from which they extend, as is indicated by the right angle in FIG. 1.

In order to be able to realize the elements 18 from FIG. 1 with the orientation which is shown there, the casting core 21 would have to have correspondingly formed and oriented recesses 22 (FIG. 2). In the case of the two-part core mold 23 of FIG. 3, corresponding mold elements 26 would have to be arranged on the mold halves 23 a and 23 b for forming the recesses 22. However, it is immediately apparent in the view of FIG. 3 that in the case of mold elements 26 which are differently orientated in such a way the two mold halves 23 a and 23 b during demolding can no longer be drawn apart in the demolding direction without the formed recesses 22 being damaged or being destroyed, or the mold elements 26 being sheared off.

In order to be able to create such differently oriented elements 18 in a simple manner and without the risk of damage within the production process for the casting core 21, however, according to FIGS. 4 and 5 provision is made for separate mold inserts 27, 28 for the region in which the elements 18 are to be arranged, which mold inserts are responsible for forming the recesses 22 and can be withdrawn separately from the mold halves 23 a and 23 b.

During the production of the casting core 21 with a core mold configuration according to FIG. 4, the mold halves 23 a and 23 b, during demolding, are first of all drawn apart in the demolding direction (vertically upwards and downwards in FIG. 4). The mold inserts 27 and 28 remain on the casting core 21 in this phase. If the mold halves 23 a and 23 b are removed, the mold inserts 27 and 28 can be withdrawn from the casting core in those directions which correspond to the orientation of the elements 18 (inclined arrows in FIG. 4). In this way, it is possible within the scope of the customary casting process to create in a simple way elements 18 in the cavity 16 of the blade 10 which are optimized for cooling and the orientation of which differs from the (main) demolding direction of the core mold.

LIST OF DESIGNATIONS

-   10 Blade (gas turbine) -   11 Leading edge -   12 Trailing edge -   13 Suction side -   14 Pressure side -   15 Wall -   16 Cavity -   17 Cooling air outlet -   18 Turbulator (pin) -   19, 20 Internal surface -   21 Casting core -   22 Recess -   23 Core mold -   23 a, b Mold halves -   24 Cavity -   25 Parting plane -   26 Mold element -   27, 28 Mold insert -   29 Rib -   30 Rib element 

1. A blade (10) for a gas turbine, said blade (10) having a leading edge (11) and a trailing edge (12), and an interior cavity (16), which is delimited by internal surfaces (19, 20), for guiding cooling air therethrough, wherein for improving the transfer of heat between a wall (15) of the blade and the cooling air, a multiplicity of members (18), which are formed on the wall (15) to improve cooling, are arranged in a distributed manner in the region of the trailing edge (12) and project from the internal surfaces (19, 20) into the cavity (16), the members (18) extend into the cavity (16) in a direction which can be freely selected within an angular range.
 2. The blade as claimed in claim 1, wherein the members are turbulators or pins (18) which extend into the cavity (16) in a direction which is essentially perpendicular to the associated internal surface.
 3. A method for producing a blade (10) for a gas turbine by a casting technique, said blade (10) having a leading edge (11) and a trailing edge (12), and an interior cavity (16), which is delimited by internal surfaces (19, 20), for guiding cooling air therethrough, wherein for improving the transfer of heat between the wall (15) of the blade and the cooling air, a multiplicity of members (18), which are formed on the wall (15) to improve cooling, are arranged in a distributed manner in the region of the trailing edge (12) and project from the internal surfaces (19, 20) into the cavity (16), the members (18) extend into the cavity (16) in a direction which can be freely selected within an angular range, the method comprising the following steps: providing a core mold (23; 23 a, b) for forming a casting core (21) which keeps the cavity (16) of the blade (10) free, producing the casting core (21) is by means of the core mold (23; 23 a, b); removing the casting core (21) from the core mold (23; 23 a, b); and casting the blade (10) by the casting core (21), wherein the core mold (23; 23 a, b) which is provided in the first step comprises two mold halves (23 a, b), which during demolding are drawn apart in a first direction, wherein at least one mold insert (27, 28), which is provided for forming the members (18), is arranged in the mold halves (23 a, b) in the trailing edge region, and in the third step, after the parting of the mold halves (23 a, b) in the first direction, the at least one mold insert (27, 28) is withdrawn from the formed casting core (21) in a second direction which differs from the first direction.
 4. The method as claimed in claim 3, wherein the second direction is perpendicular to the internal surface (19, 20) which is associated with the members (18).
 5. The method as claimed in claim 3, wherein a plurality of mold inserts (27, 28) are arranged in the mold halves (23 a, b) and during demolding are withdrawn from the formed casting core (21) in different directions which differ from the first direction. 